The present invention relates to scanning micro-electro-mechanical systems (MEMS) mirrors using a motor to drive at least part of a mirror""s movement.
Movable mirrors are often used to scan a reflected laser beam in systems such as bar code readers and in laser printers. One common way to provide a movable mirror is to have a spinning polygonal body having mirrored or highly reflective surfaces. One of the downsides to the spinning polygon mirror is that it only scans across in one direction. Another downside to the spinning polygon mirror is the spin-up time required to get the polygonal body spinning at, the needed angular velocity, which is typically more than 50 milliseconds. In addition, polygon mirrors are known to be noisy devices. There is a need for a movable mirror device with a quicker spin-up time (i.e., less than 50 milliseconds).
Magnets and/or electromagnets are sometimes used for driving the movement of a mirror. Often magnetically driven mirrors have one or more magnets attached to the mirror. There are several downsides to attaching one or more magnets to the mirror. One downside is that magnets add cost to the device. Not only does the magnetic material add cost, but the procedure and tooling to accurately mount the magnet may add cost. Magnet mounting may induce asymmetric forces that distort the mirror. Also, magnet mounting may induce thermal stresses that distort the mirror. Also, many current designs lack rotational stops, which reduces robustness of the device. Hence, there is a need for a movable mirror system that addresses these shortcomings.
The problems and needs outlined above are addressed by embodiments of the present invention. In accordance with one aspect of the present invention, a movable mirror device is provided. The movable mirror device includes a sheet, a magnetic flux channeling circuit, and a wire of electrically conducting material. The sheet has a frame portion, a hinge portion, and a mirror portion formed therein. The sheet may comprise a silicon based material, for example. The hinge portion has a pivot axis. The mirror portion is coupled to the frame portion via the hinge portion so that the mirror portion can pivot about the pivot axis relative to the frame portion. The hinge portion is twisted when the mirror portion pivots about the pivot axis and the twisted hinge portion biases the mirror portion toward a neutral relaxed position where the mirror portion is substantially aligned with a plane of the frame portion. The mirror portion has a first side and a second side. The frame portion at least partially borders the mirror portion.
The magnetic flux channeling circuit includes four circuit portions. The portions of the magnetic flux channeling circuit may comprise a nickel-iron alloy, for example. The first circuit portion is attached to the first side of the mirror portion, and the first circuit portion is separated from the remainder of the magnetic circuit portions when the mirror portion is in the neutral position. The second circuit portion extends on the first side of the mirror portion. An end of the second circuit portion is separated from the first circuit portion by a first spaced distance when the mirror portion is in the neutral position. The third circuit portion extends on the second side of the mirror portion. An end of the third circuit portion is separated from the second side of the mirror portion by a second spaced distance when the mirror portion is in the neutral position. The wire is coiled about the fourth circuit portion such that a magnetic field is induced within the fourth circuit portion and through the magnetic flux channeling circuit when electrical current flows through the wire.
There are many possible configurations for the arrangement of the magnetic circuit portions, and hence many possible embodiments. For example, the second, third, and fourth circuit portions may be part of a single piece, such that magnetic flux may flow through the magnetic flux channeling circuit from the fourth circuit portion to the second circuit portion, to the first circuit portion, to the third circuit portion, and back to the fourth circuit portion to complete one circuit loop. The magnetic circuit may include one or more additional magnetic circuit portions. For example, the magnetic flux channeling circuit may further include a fifth circuit portion attached to the second side of the mirror portion, wherein the end of the third circuit portion is separated from the fifth circuit portion by a third spaced distance when the mirror portion is in the neutral position. In such case, the magnetic flux may flow through the magnetic flux channeling circuit from the fourth circuit portion to the second circuit portion, to the first circuit portion, to the fifth circuit portion, to the third circuit portion, and back to the fourth circuit portion to complete one circuit loop.
As another example, the magnetic flux channeling circuit may further include a sixth circuit portion, a seventh circuit portion, a eighth circuit portion, a ninth circuit portion, and a tenth circuit portion. The sixth circuit portion may be attached to the first side of the mirror portion, such that the sixth circuit portion is separated from the remainder of the magnetic circuit portions when the mirror portion is in the neutral position. The seventh circuit portion may be attached to the second side of the mirror portion, such that the seventh circuit portion is separated from the remainder of the magnetic circuit portions when the mirror portion is in the neutral position. The eighth circuit portion may extend on the first side of the mirror portion, such that an end of the eighth circuit portion is separated from the sixth circuit portion by a fourth spaced distance when the mirror portion is in the neutral position. The ninth circuit portion may extend on the second side of the mirror portion, such that an end of the ninth circuit portion is separated from the seventh circuit portion by a fifth spaced distance when the mirror portion is in the neutral position. The tenth circuit portion may extend between and connect the third circuit portion to the ninth circuit portion. In such case, the second circuit portion, the fourth circuit portion, and the eighth circuit portion form a single piece, and the third, ninth, and tenth circuit portions form another single piece. Hence in such case, the magnetic flux may flow through the magnetic flux channeling circuit from the fourth circuit portion to the second circuit portion, to the first circuit portion, to the fifth circuit portion, to the third circuit portion, to the tenth circuit portion, to the ninth circuit portion, to the seventh circuit portion, to the sixth circuit portion, to the eighth circuit portion, and back to the fourth circuit portion to complete one circuit loop.
The ends of the second and eighth circuit portions may provide a first set of pivot stops to limit the pivotal movement range of the mirror portion in a first angular direction. Similarly, the ends of the third and ninth circuit portions may provide a second set of pivot stops to limit the pivotal movement range of the mirror portion in the first angular direction. The pivotal movement range of the mirror portion in the first angular direction from the neutral position may be about 15 degrees, for example. Preferably, the device is adapted to allow the mirror portion to pivot a total of about 30 degrees.
A laser printer device, a bar code scanner system, or a digital light projector may be provided that incorporates a movable mirror device in accordance with the present invention, for example.